The present invention relates to an improved process and an improved device for orienting individual fibres and/or filaments present in a web, in particular derived from a card.
Usually, webs intended to be worked in order to obtain tufted, stitched, knitted or other products, are prepared by carding followed by drawing in a direction orthogonal to the outlet of the card. It is usually observed that the average orientation angle of the fibres in a web leaving the card is about xc2x15 degrees relative to the feed direction.
To modify the value of the angle, it might be proposed to draw said web. In this case, the value of the angle after drawing corresponding to the new orientation xcex1, which is defined orthogonally relative to the feed direction of the web, is given by:
tg(xcex1)=e tg(5xc2x0),
where e is the ratio of the widths of the web before and after transverse drawing.
Another possibility consists in proposing to carry out a passage through a spreading-lapping machine in order to produce a lap comprising several folds, as described, for example, in document EP-A-0 520 911. Preferably, this lapping step is carried out prior to the passage through a drawing machine.
Moreover, the Applicant has developed a particular technique known as the xe2x80x9cverticalization techniquexe2x80x9d for producing textile products from a web of individual fibres and/or filaments. This technique has already been the subject of many publications since 1991, and has been described in particular in documents WO91/00382, WO96/10667, WO97/05315 and WO98/36119. It consists in proposing the preparation of a textile product directly from fibres and/or filaments travelling in the feed direction in the form of a web, this process comprising at least one step known as a xe2x80x9clooping stepxe2x80x9d in which the fibres and/or filaments are individually submitted to a looping transversely relative to the feed direction of the web, optionally accompanied by a transverse drawing.
This technique allows to produce textile products intended for producing floorcoverings in the form of a tuft as described in document WO91/00382, the production of stitched products as described in document WO96/10667 or the production of lapped products as described in document WO98/36119.
Nevertheless, to work this verticalization technique, it is important for the starting web of fibres and/or filaments to have a low weight per unit area (preferably of between 10 and 50 g/m2). Moreover, it is necessary for most of the constituent elements of the web, that is to say the fibres and/or filaments, to have an angle of orientation relative to the feed direction of the web of between 5 and 45 degrees, and preferably between 15 and 25 degrees.
With this aim, and in particular in document WO91/00382, a pre-drawing step has been included in order for the elements constituting the web (the fibres and/or filaments) to have the correct angle of entry before undergoing said verticalization step which consists in individually imparting to the constituent elements of the web transverse looping accompanied by drawing and followed by accumulation of said fibres and/or filaments which have been parallelized in a particularly satisfying manner in the form of loops so as to make a pseudo-yarn.
The pre-drawing step consists in passing a web of low surface density into a set of interpenetrating discs which oblige the web, optionally derived from the card, to undergo looping over a width greater than that of the product to be made. The fibres are then left to recover, by resilience, a flat position which they obtain by stretching widthwise, allowing the fibres to pivot towards a new orientation.
As described in document WO91/00382, this pre-drawing step consists in submitting the web to a set of discs spaced apart by a distance j (gauge), which are arranged on two shafts. The discs on the two shafts are positioned in a staggered arrangement relative to each other and interpenetrate over a distance d which allows the amplitude of the looping and thus the drawing value to be defined, i.e. exe2x89xa12j/d and thus allows xcex1 to be defined.
The device described in the prior art has proved itself and demonstrated its efficiency in an industrial context. Nevertheless, a certain number of drawbacks remain, in particular:
In the case of a high value of e: in this case, the resilience of the fibres reaches its limit. Beyond e=2, the undulations have a tendency to be converted into folds and to persist in the drawn web, thus creating irregularities.
In the case of large working widths: for widths greater than 4 m, an undulation generated at the centre of the web can only be xe2x80x9crelaxedxe2x80x9d by pushing its neighbours. In this case, the intrinsic resilience of the fibres contained in a single undulation will be insufficient to push the entire width of the web. It also depends greatly on the type and nature of the fibres used.
When it is desired to obtain a value of e which can be modulated over the width of the web, which may prove to be very useful when it is desired to correct the weight curves of the web: specifically, the web has a tendency to be slightly heavier at the centre than on the sides.
When it is desired to generate webs starting with elements that are very narrow, such as tapes, filaments or cables.
Firstly, the present invention aims to propose a solution for modifying the width of the web, optionally derived from the card.
More particularly, the present invention aims to propose a web which will undergo the verticalization process and in which the individual fibres and/or filaments have the appropriate orientation.
The present invention aims also to allow, besides an appropriate orientation of the fibres within said web, an isotropic orientation of said fibres.
Finally, the present invention aims additionally to allow the production of a web which has a condensation of fibres, in particular in the case of a preparation of a dense product.
The present invention relates to a process for obtaining an appropriate orientation of constituent elements of a web, such as fibres and/or filaments, for example derived from a card, characterized in that:
the fibres and/or filaments are submitted to a pre-looping step carried out by means of the interpenetration of a first set of looping discs carried on a common transverse shaft and driven in continuous rotation at a first speed, and of a first set of fixed looping elements, the set of looping discs and the set of looping elements having a defined gauge j so as to cause the fibres and/or filaments to be pre-looped with an undulation value or period j,
with the aid of blocking means, said fibres and/or filaments are held at regular intervals of a length of (nxc3x97j) where n is an integer between 2 and 20,
the pre-looped fibres and/or filaments are allowed to expand so as to produce large undulations with an undulation value or period (nxc3x97j), and
the pre-looped fibres and/or filaments are spread by simple transverse drawing over an undulation value or period (nxc3x97j).
The present invention also relates to the device for carrying out this process, characterized in that it comprises:
a first set of looping discs carried on a common transverse shaft and driven in continuous rotation at a first speed,
a first set of fixed looping elements, the set of looping discs and the set of looping elements having a defined gauge (j) so as to cause the fibres and/or filaments to be pre-looped with an undulation value or period (j),
blocking elements regularly arranged with a gauge (nxc3x97j) where n is an integer between 2 and 20, which are intended to block the pre-looped fibres and/or filaments over an undulation value or period (j) at regular intervals of a length (nxc3x97j), and
a spreading conveyor for flattening out the fibres and/or filaments.
Preferably, said looping elements of the device are looping fingers.
According to a first embodiment, said blocking elements consist of looping fingers that are longer than the other looping fingers and are present every 2 to 20 consecutive looping fingers.
According to a second embodiment, these blocking elements consist of another set of detaching discs carried on a common transverse shaft and driven in continuous rotation at a speed corresponding to the rotation speed of the looping discs.
Advantageously, in this embodiment, the detaching discs are arranged in the extension of some of the looping fingers.
Advantageously, the spreading conveyor consists of a set of individual belts arranged divergently, and the number of these individual belts preferably corresponds substantially to the number of blocking elements.
Advantageously, the blocking elements penetrate slightly between the various individual belts.
Preferably, mechanical means are provided to vary the longitudinal speeds of the belts slightly, such that the travelling speed at any transverse point of the web is equivalent for all the belts.
Advantageously, the device of the invention also comprises means for condensing the fibres and/or filaments arranged upstream the first set of looping discs and the first set of fixed looping elements.
These fibre-condensing means preferably consist of a second set of looping discs carried on a second common transverse shaft and driven in continuous rotation at a speed and between which are arranged fixed looping elements forming a second set of looping elements. The second set of looping discs and the second set of fixed looping elements have the same gauge as the first set of looping discs and the first set of fixed looping elements, and the rotation speed of the second set of looping discs is greater than that of the first set of looping discs.